The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Particle agglomeration is a natural phenomenon that may be described as the flocculation or coalescence of individual particles or particle aggregates that occurs in powders or finely-divided particles in bulk solid form or upon attempting to disperse such finely-divided particles into a liquid or flowable medium, such as a solvent, a polymer, a plastic, or an elastomeric matrix. In some instances, the surface energy of the particles is lower than the magnitude necessary for the particles to be properly dispersed in the flowable medium. In powders, the occurrence of agglomeration can be undesirable resulting in uncontrolled build-up, caking, bridging, or lumping. Similarly, the occurrence of particle agglomeration during the dispersion of finely-divided particles in a liquid or flowable medium may undesirably affect the material properties associated with the dispersion, such as color strength, viscosity, texture, compressibility, abrasiveness, and reactivity, to name a few.
The effective use of particle dispersions in many applications requires that the formation of particle agglomerates during the dispersion process be either all together avoided or minimized, such that any agglomerates that are formed can be subsequently broken-down into individual particles or particle aggregates without damaging the particles. For example, coating formulations that exhibit high brilliance and color strength are characterized by the degree of individual pigment dispersion, pigment particle size, and long-term stabilization of the dispersed pigments in the liquid carrier fluid.
The break-up of agglomerated particles may be accomplished through the use of various mechanical mixing techniques, such as media milling, high shear mixing, or ultrasonication. The break-up of agglomerates using these techniques is controlled predominantly by the amount of energy input. For example, during media milling, the break-up of particle agglomerates occurs due to the impact between the agglomerates and the milling media and by the creation of high shear rates. Although the use of these techniques can be effective in reducing particle agglomerates, these techniques also are time consuming, increase production costs, alter the shape or grain structure of the individual particles or particle aggregates, and/or introduce contaminants into the dispersion or finished product composition.
The dispersion of individual particles or particle aggregates in a liquid or flowable medium represents a technical problem which is difficult to solve because flocculation or agglomeration is a phenomenon that can occur in the bulk solid or powder and is difficult to break-up after its occurrence without altering or damaging the individual particles or particle aggregates.